Abstract

Background The barrier function of the skin may be characterised by a number of biophysical and molecular methods. Variation in the barrier properties as a function of depth has not been explored in detail. Objectives The aim of the present study was to characterise changes in corneocyte surface area, corneocyte maturity, selected protease activities and Trans-epidermal water loss (TEWL) in the ventral forearm with increasing depth. Methods The left mid-ventral forearm of 22 healthy volunteers was selected as the study site. After tape-stripping, corneocyte maturity and surface area were assessed. The protease activity of the desquamatory kallikrein proteases, KLK5 and KLK7 as well as tryptase was measured using a fluorogenic probe assay. Protein content and Trans-epidermal water loss was also recorded. Results Corneocyte maturity and surface area decreased with increasing number of tape strippings, i.e. depth into the skin. More mature corneocytes were typically larger than less mature corneocytes. The protease activities of both the desquamatory and inflammatory enzymes together with the protein content were highest in the outer layers of the stratum corneum and decreased with depth. As expected, TEWL increased as more stratum corneum layers were removed. There were no statistical differences between males and females or Caucasian and Black subjects for all of the parameters studied. Conclusions The techniques used in this study provide rapid non-invasive measures of the spatial distribution of corneocyte maturity and surface area as well as protease activity and protein content within different levels of the stratum corneum layers. The methods used will allow mechanistic insight into the effects of formulation excipients and actives on epidermal turnover and skin barrier function.